Create easily reusable character for still images
Well, in fact what you are asking is something easily accomplishable whit the correct rigging technique and enough patience to pose the characters, animation and posing are areas that require patience to get things correctly done, so keep that in mind.

But if your models are simple enough in terms of polygon count, you could easilyuse shape keys to make transitions between poses:
http://www.chocofur.com/using-shape-keys-in-blender.html

Here is a tutorial where you can get started, but remember, nothing is better for posing that rigging.